PROJECT SUMMARY: Early undernutrition is highly prevalent in low- and middle-income countries (LMICs) and it is widely claimed that unless undernutrition is addressed in the first 1,000 days, it has long-lasting and almost irreversible consequences. Climatic variation also is considerable in many LMICs and widely claimed to have substantial impacts on child development, with long-run consequences. However, there is little population-based evidence about mechanisms through which early-life undernutrition and climatic variations lead to poorer adolescent and adult outcomes and whether early-life deficits may be mitigated. This project will investigate the potential impact of undernutrition and climatic variations on a set of foundational cognitive skills (FCS), importantly including executive function (EF), which remains malleable throughout childhood and adolescence. EF increasingly has been found to be a key domain of child development and a key predictor of educational success and possibly correlated with non-cognitive skills development and risky behaviors. However, most evidence comes from high- income countries (HICs) and there is very little evidence about the determinants of and the impacts of FCS in LMICs, where conditions are much different (e.g. greater early-life undernutrition and climatic variations). The Specific Aims (SA) are to investigate: (SA1) the determinants of FCS in late childhood, including (SA1a) early- life nutrition; (SA1b) climatic variations; and (SA1c) social policies; and (SA2) the impacts of late childhood FCS on adolescent educational achievements, socio-emotional competencies and risky behaviors. Each of these specific aims will examine differences for boys versus girls. The project will use unique data on a set of FCS measures collected in Ethiopia and Peru as part of the Young Lives Study (YLS), the largest multi-country cohort dataset on childhood poverty and wellbeing in LMICs. That the YLS data are longitudinal and comparable measures have been collected across very different countries make these data uniquely well-suited for examination of longer-term impacts of early-life deficits on a variety of outcomes measured at ages 5,8,12 and 15 years. The data collected in 2013 for ~4,000 children in Ethiopia and Peru and ~2,000 of their immediate siblings included RACER (Rapid Assessment of Cognitive and Emotional Regulation), a novel touch-screen computer application designed to obtain measurements of a set of FCS: working memory, inhibition (both of which are considered EF), declarative memory and implicit learning. These data are unique, rarely available from LMICs and not previously available for large samples. The analysis promises significant contributions for (1) deeper understanding of how early-life nutrition, climatic variations and other events affect FCS, (2) how policy interventions can help mitigate the effects of early childhood poverty through affecting EF in contexts of two countries at very different stages of economic and social development, (3) what are the impacts of late childhood FCS on adolescent outcomes, and (4) assessing the value of undertaking similar data collection and analysis at other ages and in other LMICs, possibly including the other YLS countries, India and Viet Nam.